Microglia Overexpressing the Macrophage Colony-Stimulating Factor Receptor Are Neuroprotective in a Microglial-Hippocampal Organotypic Coculture System

Abstract

Microglia with increased expression of the macrophage colony-stimulating factor receptor (M-CSFR; c-fms) are found surrounding plaques in Alzheimer's disease (AD) and in mouse models for AD and after ischemic or traumatic brain injury. Increased expression of M-CSFR causes microglia to adopt an activated state that results in proliferation, release of cytokines, and enhanced phagocytosis. To determine whether M-CSFR-induced microglial activation affects neuronal survival, we assembled a coculture system consisting of BV-2 microglia transfected to overexpress the M-CSFR and hippocampal organotypic slices treated with NMDA. Twenty-four hours after assembly of the coculture, microglia overexpressing M-CSFR proliferated at a higher rate than nontransfected control cells and exhibited enhanced migration toward NMDA-injured hippocampal cultures. Surprisingly, coculture with c-fms-transfected microglia resulted in a dramatic reduction in NMDA-induced neurotoxicity. Similar results were observed when cocultures were treated with the teratogen cyclophosphamide. Biolistic overexpression of M-CSFR on microglia endogenous to the organotypic culture also rescued neurons from excitotoxicity. Furthermore, c-fms-transfected microglia increased neuronal expression of macrophage colony-stimulating factor (M-CSF), the M-CSFR, and neurotrophin receptors in the NMDA-treated slices, as determined with laser capture microdissection. In the coculture system, direct contact between the exogenous microglia and the slice was necessary for neuroprotection. Finally, blocking expression of the M-CSF ligand by exogenous c-fms-transfected microglia with a hammerhead ribozyme compromised their neuroprotective properties. These results demonstrate a protective role for microglia overexpressing M-CSFR in our coculture system and suggest under certain circumstances, activated microglia can help rather than harm neurons subjected to excitotoxic and teratogen-induced injury.

Selective Ablation of Proliferating Microglial Cells Exacerbates Ischemic Injury in the Brain

“…Interestingly, the absence of M-CSF and microglial proliferation was associated with enhanced neuronal sensitivity to injuries and increased neuronal cell death after cerebral ischemia (Berezovskaya et al, 1996;Fedoroff et al, 1997). Conversely, addition of M-CSF conferred neuroprotection in the microglialhippocampal organotypic coculture system (Vincent et al, 2002;Mitrasinovic et al, 2005). At present, the mechanism of M-CSF neuroprotection remains unclear.…”

Microglia Cells Protect Neurons by Direct Engulfment of Invading Neutrophil Granulocytes: A New Mechanism of CNS Immune Privilege

“…In an attempt to overcome this limitation, we chose to use a well established ex vivo model of neuroinflammation (Ullrich et al, 2001;Mitrasinovic et al, 2005;Neumann et al, 2006). Using this model, we were now able to demonstrate that indeed only PMNs sharply increased neuronal damage associated with transient ischemia.…”

“…Several studies demonstrated the neurotoxic properties of activated microglia after ischemic or excitotoxic damage (Giulian et al, 1993;Kim and Ko, 1998;Rogove and Tsirka, 1998;Yrjanheikki et al, 1999), whereas considerable evidence shows that microglia triggered by injured/dying neurons mediate a reduction of neuronal damage and induction of tissue repair (Morioka et Considering these controversial findings on the role of PMNs and microglia during transient ischemia, strikingly few studies have evaluated the direct effect of these immune cells on neuronal survival/damage (Dinkel et al, 2004;Mitrasinovic et al, 2005). Despite that, although the combined recruitment of both cell types to tissue sites affected by cerebral ischemia is well established, a potential direct interaction of both immune cell types has not been investigated in depth.…”

Anti-inflammatory effect of stem cells against spinal cord injury via regulating macrophage polarization

“…29 The result indicates that activated macrophages at the injured site could provide a beneficial microenvironment, which is good for regeneration of sensory axons, possibly due to the release of transforming growth factor-b (TGF-b). 30 Mitrasinovic et al 31 showed…”